PHREEQ C Modelling Tool Application to Determine the metal Speciation Effect on water quality

What is it about?

The study aims to use the PHREEQC modelling tool to examine how various anions in water affect the chemical speciation (forms) of certain heavy metals in water sources in the study area. Speciation affects metal mobility, toxicity, and bioavailability. Methods Sampling: Water samples collected from different sources (surface water, boreholes, dams) in Kajiado North. Analyses: Measured parameters included pH, temperature, electrical conductivity; metal ions and various anions (chlorides, sulfates, nitrates etc.) using methods like ICP-OES, photometry etc. Modelling: PHREEQC was used to model how anions influence metal speciation under the observed water chemistry. This included seeing how pH, temperature, anion concentration changes shift metal species. Key Findings Some sampled water sources had heavy metal concentrations that are concerning, given their possible health effects. The presence and concentration of specific anions had a noticeable effect on which chemical forms (species) the metals took. For example, certain metals were more present in forms complexed with carbonate, sulfate, or hydroxide depending on water chemistry (pH, temperature etc.). The modelling and simulations showed that as conditions (e.g. pH, anion levels) vary, the dominant species of metals shift, which has implications for how toxic or mobile those metals are. Implications / Conclusion Speciation modelling is valuable: you can’t just measure total metal concentration — knowing the form matters for assessing risk. Some water sources may be at risk of exposure to toxic metal species under certain conditions. Management of water quality should consider not just reducing total metal loads, but also controlling anion concentrations, pH etc. Recommendations are likely toward monitoring water chemistry parameters (anions, pH, temperature), regular testing, and perhaps treatment to adjust speciation in unsafe sources

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Photo by Norbert Buduczki on Unsplash

Photo by Norbert Buduczki on Unsplash

Why is it important?

The study on PHREEQC modeling of anion effects on metal speciation in water systems in Kajiado North remains highly relevant today for several reasons: Water Quality and Public Health Kajiado North, like many semi-arid regions in Kenya, depends on groundwater and surface water that may be contaminated with trace metals. Understanding how anions (e.g., fluorides ,chloride, sulfate, bicarbonate) influence metal mobility and toxicity helps assess health risks, since speciation determines whether metals are bioavailable or less harmful. Environmental Protection Speciation studies guide pollution control and remediation strategies. For example, knowing that certain anions stabilize toxic free-metal ions can shape interventions to protect aquatic ecosystems. Agricultural Relevance Communities in Kajiado rely on irrigation. Metal speciation affects not just water safety for consumption but also soil chemistry and crop uptake of metals, with long-term food safety implications. Policy and Regulation Kenya’s water policies and county-level environmental monitoring increasingly require data-driven management. Modeling tools like PHREEQC provide evidence for regulatory standards and safe discharge limits. Climate Change and Water Stress With changing rainfall patterns, reliance on groundwater will increase. Predictive modeling of how chemical interactions evolve under varying conditions is critical for sustainable water management. Global Scientific Relevance The study adds to broader research on metal-anion interactions in hydrogeochemistry, a subject important for mining regions, urbanization impacts, and safe water supply across Africa and beyond

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